1. Technical Field of the Invention
The present invention relates to a control system, an electronic control unit, and a communication method. The control system includes a plurality of sensors and the electronic control unit.
2. Related Art
In the technical field of vehicle control, drive units are conventionally known into which a sensor and an actuator are integrated. As an example of the drive units, a unit is known in which a memory is included for storing individual characteristic values, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-057413.
Initial characteristic values are written into the memory of the drive unit when the product is shipped. The characteristic values are used in an electronic control unit (ECU) for controlling the drive unit.
In addition, a technique is known in which learning values obtained by an electronic control unit are written into a memory of a drive unit to prevent loss of the learning values due to replacement of the electronic control unit or the like.
Incidentally, when using techniques in which an actuator and a memory are integrated and initial characteristic values or learning values are written into the memory, an electronic control unit is required to read the initial characteristic values from a drive unit or write the learning values into the drive unit. Therefore, the drive unit is required to be provided with a communication function.
A method can be provided for connecting a plurality of drive units to an electronic control unit to enable the communication therebetween. According to the method, for example, the drive units are connected to the electronic control unit via individual communication lines. When using such a method, the electronic control unit is required to be provided with individual communication devices for the drive units. Therefore, the drive units are preferably connected to the electronic control unit via a common communication line, that is, a bus.
However, when using the method by which the bus communication is used, individual node IDs are assigned to the drive units to perform communication between the electronic control unit and the drive units depending on the node IDs. Therefore, when the node IDs are incorrectly assigned to the drive units, disadvantages arise.
As an example, a case will be considered where injectors for cylinders are connected to an electronic control unit via a common communication line. Fuel injection through the injectors is controlled, as is well known, in such a manner that an injection signal is outputted from the electronic control unit to an electronic drive unit (EDU), and the electronic drive unit drives the injector based on the injection signal. That is, the fuel injection through the injectors is controlled via a line different from that used for memory access performed from the electronic control unit to the injectors via the communication line.
Hereinafter, a case is considered where an electronic control unit obtains characteristic values from injectors via a communication line on the assumption that a node ID of “1” is assigned to an injector of a first cylinder and a node ID of “2” is assigned to an injector of the a second cylinder. However, in this case, the injector to which the node ID “2” is assigned could be incorrectly mounted in the first cylinder and the injector to which the node ID “1” is assigned could be incorrectly mounted in the second cylinder.
In the above case, the electronic control unit reads a characteristic value of the injector of the second cylinder as a characteristic value of the injector of the first cylinder from the injector to which the node ID “1” has been assigned and which is mounted in the second cylinder. Then, the electronic control unit controls the injector of the first cylinder based on the characteristic value read. This cases problems with control.
Problems similar to the above case are also caused in a case where a sensor signal indicating a physical quantity measured by a sensor is received by an electronic control unit as an analog signal without a communication line. As an example, a case will be considered where individual signal lines, which transmit sensor signals, are provided for drive units in addition to the communication line.
In this case, although the connection relationship between the sensor included in the drive unit and the electronic control unit is physically determined by the signal line, the connection relationship between a memory included in the drive unit and the electronic control unit is logically determined by a node ID.
Consequently, in a system in which a sensor included in a drive unit having a node ID of “1” should be connected to a first signal line and a sensor included in a drive unit having a node ID of “2” should be connected to a second signal line, when the sensor included in the drive unit having the node ID of “2” is incorrectly connected to the first signal line and the sensor included in the drive unit having the node ID of “1” is incorrectly connected to the second signal line, the electronic control unit corrects a sensor signal received via the first signal line from the drive unit having the node ID of “2” and connected to the first signal line based on a characteristic value obtained via the communication line from the drive unit having the node ID of “1” and connected to the second signal line. This cases a problem that physical quantity measured by the sensor cannot be correctly corrected.